Top image by researcher Ross Wanless shows an R.O.U.S. consuming the remains of a dead seabird chick, via National Geographic

The massacre is taking place on Gough Island (map), a British territory almost smack-dab in between the tips of South America and South Africa. The only humans living on the island belong to a small team running a weather station.

Gough Island has long been recognized as an important seabird colony, since it hosts roughly ten million birds of more than 20 species. The island is also thought to be the only breeding ground for the Atlantic petrel-2 million breeding pairs produce 1.6 million chicks a year.

The new study, though [published by researcher Ross Wanless and colleagues in a recent issue of Animal Conservation], reveals that the petrel chicks are in constant danger from house mice, which have grown to supersize proportions since being introduced to the island 150 years ago.

How supersized are we talking? Let's put it this way: R.O.U.S.s do exist, and they're ravaging Gough island.

Gough is a textbook example of what can happen when a nonnative species is introduced to an ecosystem devoid of predators and rich in resources. These mice are up to 50% larger than normal mice (some measure up to ten inches in length without their tails), and their population levels have exploded, reaching what Wanless calls "stupendous densities" every summer (about 1.9 million mice on an island just 25 miles2 in area). This massive growth in size and population has enabled them to overwhelm larger birds like petrels and albatrosses. It's been so overwhelming, in fact, that Wanless and his colleagues think these rare birds may face serious risk of extinction.